1. Field of the Invention
Alkenyl-substituted dicarboxylic acids and their derivatives are valuable additives for fuels and for lubricating oil compositions. The basic reaction is well known and involves the reaction of a polyolefin with an unsaturated dicarboxylic acid anhydride, such as maleic anhydride, to produce the corresponding alkenyl-substituted dicarboxylic acid anhydride.
The polyolefin-dicarboxylic anhydride reaction does not proceed cleanly nor does it give theoretical results. On the contrary, the yields are less than can be desired and the reaction often results in the production of sludge or tarry residues which must be separated from the reaction product. It has been postulated that the unsaturated dicarboxylic acid anhydride reactant polymerizes and decomposes under the reaction conditions employed leading to the production of sludge or tarry residues.
2. Description of the Prior Art
Numerous processes have been developed to improve the yield of the polyolefin-dicarboxylic acid anhydride reaction. U.S. Pat. No. 3,927,041 discloses the reaction of viscous polybutenes with unsaturated aliphatic dicarboxylic acid anhydrides in the presence of a brominated dialkyl hydantoin. The use of a brominated dialkyl hydantoin is disclosed to reduce the formation of undesirable by-products resulting from polymerization and/or thermal decomposition of the unsaturated anhydrides. The use of certain dibrominated dialkyl hydantoins results in the production of an acceptable yield of alkenyl-substituted dicarboxylic acid anhydride based on the amount of the starting polymer.
U.S. Pat. No. 4,086,251 discloses a process for manufacturing a polyalkenyl succinic anhydride in the presence of an additive which suppresses the formation of tarry materials and undesirable reaction side products and/or improves yield in which a portion of the recovered unsaturated intramolecular anhydride is recycled to the reaction zone. This reference also discloses the use of reaction modifying additives including chlorinated and brominated aliphatic hydrocarbons, chlorine and/or bromine-containing derivatives of carboxylic or sulfonic acids, chlorinated and/or brominated anhydrides of aliphatic carboxylic acids, chlorinated and/or brominated aliphatic or aromatic ketones and acetals, and the above-noted dibromo-dialkyl substituted hydantoin.